The invention relates to an earth boring device and a threaded element with a thread retention for an earth boring device.
Earth boring devices, in particular in the field of trenchless installation and rehabilitation of lines and pipes, are known in many forms.
One type of earth boring devices involves so-called soil displacement hammers, which are characterized by an internal percussion drive having a percussion piston which oscillates, i.e. strikes alternately, inside a housing of the soil displacement hammer and is operated by a pressure fluid and which impacts—depending on the feed direction of the soil displacement hammer—a leading or trailing impact surface of the housing or an attached structure and thereby transfers its kinetic energy onto the earth boring device for propelling the latter into the earth.
The impact surfaces of the percussion piston as well as of the housing must evidently withstand very high stress. Therefore, the impact surfaces of the percussion piston and the housing are hardened. Furthermore, it may be provided to integrate at least the leading impact surface of the housing in a structure which is replaceable, when worn out. In this way, maintenance costs of the soil displacement hammer can be limited. Such a replaceable structure thus assumes the task of transferring the impact energy from the percussion piston to the housing. As a result, the connection thereof with the housing has to meet stringent requirements.
Conventionally, such replaceable structures having an impact surface are normally connected to the housing through intervention of a thread, wherein the threaded connection is oftentimes further secured by means of a thread retention adhesive. This prior art solution suffers shortcomings in operation. Firstly, hardening of the thread retention adhesive requires a wanted time period during which the soil displacement hammer cannot be operated for safety reasons. Such a delay causes added operating costs in particular when the percussion structure is replaced during a drilling need. Moreover, detachment of a percussion structure that has been secured by a thread retention adhesive is very difficult.